The present invention relates to an apparatus for separating image transfer material in an electrophotographic copying machine.
Various copying methods have been adopted in copying machines, in particular, in electrophotographic copying machines. The conventional copying methods of electrophotographic copying machines can be roughly classified into a visible image transfer type and a latent electrostatic image transfer type.
In the visible image transfer type copying method, a latent electrostatic image is formed on the surface of a photoconductor and the latent electrostatic image formed on the photoconductor is developed to a visible image and the visible image is then transferred to an image transfer material.
In the latent image transfer type copying method, the latent electrostatic image formed on the photoconductor is transferred to an image transfer material and the latent electrostatic image transferred to the image transfer material is then developed to a visible image.
In both image transfer copying methods, the step for separating the image transfer material, which is moved in uniform contact with the surface of the photoconductor, from the surface of the photoconductor after image transfer is very important and many varities of apparatus for performing the separation of the image transfer material from the photoconductor have been proposed.
An example of an image transfer material separation apparatus in general use employs a pick-off pawl with a top pawl portion thereof brought into contact with the surface of the photoconductor for picking the image transfer material off the surface of the photoconductor. In an image transfer material separation apparatus of this type, it is required that the top pawl portion be extremely sharp. Otherwise, proper and smooth separation of the image transfer material from the surface of the photoconductor cannot always be done. However, the sharper the top pawl portion, the greater the separation performance, but the greater the risk of the surface of the photoconductor being scratched by the top pawl portion or of the top pawl portion being abraded, resulting in significant decrease in separation performance of the pick-off pawl.
Another conventional example of the image transfer material separation apparatus has a pick-off pawl which is in a groove formed in the peripheral surface of a photoconductor drum in the axial direction thereof. In this image transfer material separation apparatus, it is required that the phoconductor drum be extremely accurately positioned at its home position. In order to attain such accurate positioning of the photoconductor drum, a complicated mechanism and control thereof are required.
In a further conventional image transfer material separation apparatus, for instance, one disclosed in U.S. patent application Ser. No. 219,258 filed Dec. 12, 1980 which is a continuation-in-part of application Ser. No. 213,650 filed Dec. 5, 1980 and now abandoned, a leading edge portion of the image transfer material is bent upwardly before the material reaches the image transfer station so as to be separated from the surface of the photoconductor during image transfer. The separated leading edge portion of the image transfer material is maintained away from the surface of the photoconductor and a pick-off pawl is disposed so as to be always in contact with the surface of the photoconductor, so that as the image transfer material is moved together with the photoconductor, the separated portion of the image transfer material is scooped up by the pick-off pawl and the image transfer material is then completely separated from the surface of the photoconductor. After separation of the image transfer material from the photoconductor, the image transfer material is transported by an image transfer material transportation device.
In this image transfer material separation apparatus, a charging apparatus comprising an image transfer charger and a separation charger is employed. The separation charger serves to assist in the separation of the image transfer material from the surface of the photoconductor. However, when the voltage applied to the separation charger is low, the electrostatic attraction of the image transfer material to the surface of the photoconductor cannot be decreased enough so that the image area of the image transfer material may be scratched by an edge portion of the pick-off pawl and the image quality may be considerably degraded. In contrast to this, when the voltage applied to the separation charger is high, toner images formed on the image transfer material may separate from the surface of the image transfer material and deposited on the surface of the photoconductor.
Furthermore, when voltage applied to the separation charger is varied, the position of the leading edge of the image transfer material becomes unsteady after the image transfer material is separated from the surface of the photoconductor. As a result, the direction of transportation of the image transfer material varies and the image transfer material may not be properly received by the image transfer material transportation device.
When the leading edge portion of the image transfer material is bent so as to be separated from the surface of the photoconductor, if the leading edge of the image transfer material is contained in the leading edge portion bent, wrinkling or skewing of the image transfer material may take place when the image transfer material is fed to an image fixing apparatus, in particular, to the roller-type image fixing apparatus typically used.